A conventional liquid crystal display apparatus used in, for example, a car navigation system for displaying a map or the like typically has a backlight source behind a liquid crystal display panel. It is disposed at an underside of a windshield and at an upper center of an instrument panel. The positioning of the liquid crystal display apparatus makes it easier for a driver to view an image in the apparatus because it minimizes the movement of the driver's sightline. However, an image displayed on the apparatus reflects on an inside surface of the windshield disposed over the instrument panel during night hours and interrupts the driver's view.
Another conventional apparatus disclosed in a Japanese Patent Document JP-A-H7-306411 has an optical waveguide disposed in front of a backlight source to guide a backlight perpendicular to a liquid crystal display panel. However, the optical waveguide does not effectively limit the backlight projected therethrough in an obliquely upward direction. Thus, the apparatus cannot effectively prevent reflection of the displayed image on the inside surface of the windshield.
Still other conventional apparatus disclosed in a Japanese Patent Document JP-A-H5-61034 has a polarizing film disposed between a backlight source and a liquid crystal display panel to direct the backlight perpendicular to the liquid crystal display panel. This type of polarizing film is available as a marketed product of “Light Control Film” released from corporations such as Sumitomo 3M. This apparatus substantially limits a viewing position of the liquid crystal display panel only in a front area of the apparatus for an increased visibility. Thus, it effectively prevents reflection of the displayed image on the inside surface of the windshield during night hours.
While the liquid crystal display apparatus of this kind is primarily used for driving assistance such as a map display apparatus for a car navigation system or the like, the apparatus is more frequently used for displaying different types of image sources provided as a TV program, a video program, a DVD program or the like. On the other hand, the liquid crystal display panel itself is evolving to have a wider viewing angle for viewer's convenience.
Therefore, an image on the display panel of the apparatus may be viewed obliquely upward from a lower position by a viewer (e.g., a driver or a passenger) with the viewer's seat back reclined toward a rear end of a vehicle when, for example, the vehicle is stopping in a rest area. However, the conventional apparatus having the polarizing film described above cannot accommodate this kind of situation, because the viewing position of the apparatus is strictly limited to a small area in front of the apparatus. The visibility steeply decreases if the position of the viewer moves out of the area.